Posted
by
timothyon Thursday January 31, 2013 @12:19PM
from the stay-in-sight-of-the-tower dept.

Mark.JUK writes "Scientists working at the University of Strathclyde in Scotland (United Kingdom) have begun to develop a new Light Fidelity (Li-Fi) technology that will use special micron-sized LED (Light-Emitting Diodes) lights, such as those that could be used as part of home lighting or TV displays, to form part of a sophisticated wireless communications network (much like Wi-Fi is today). The principle, which revolves around manipulating the on/off flicker of LED lights to produce a digital network (a bit like Morse Code from a torch), is not new but most of the other teams are focusing on larger Li-Fi LEDs of around 1mm square in size. However micron sized LEDs not only allow you to use more lights (each of which can act as a separate data channel) but they can also flicker on and off around 1,000 times quicker than the larger LEDs."

It is light we're talking about here, so the carrier is in the TeraHertz range, and the data frequency could be up to the Gigahertz. I'm not sure where you're confused. This won't make it through walls like Wi-Fi, but it sure will make it across an empty room.I've heard of this kind of thing before, and part of the advantage is in security - you neighbor on the other side of the wall won't be able ton intercept.

I recently tried some opto couplers (for isolation in circuits) and found that some lower grade parts work at the microsecond level but the better parts are in nanoseconds. it meant the diff of being limited at 57k via several mhz.

then again, that's inside a chip with a good path between tx and rx.

in a room, you have varying distances, reflections, obstructions.

this is going to be hard to 'get right'. I would not bet too strongly on this. rf s

It's visible light, so yeah, no penetration. TFA says it won't replace your wifi if you're looking for multi-room coverage. On the other hand, it keeps your neighbors from using (or sniffing) your net, so maybe it's a feature. (TFA also characterizes it as being useful for "broadcasting" information; use these in roadsign displays and they can shovel data on road conditions to your GPS if it has line of sight, but the earlier work it's based on did work for using the room light as a single-room WAP.)

The great side benefit of that, that nobody seems to be talking about, is that living organisms can finally start to expose themselves on a routine basis to the low-level functioning of computer communication technology. In a mere few million years, we will have evolved to the point of comprehending the flickering of the LEDs, much the same as we now comprehend written and spoken communication.

Who knows, maybe we'll even co-evolve some sort of organic signalling system of the same calibre, so we can elimina

Photosensitive epileptics are affected by high contrast, relatively low frequency flashes (well below 100Hz). A tiny LED switching so fast the most anyone is likely to see is a slight fluctuation in brightness (presuming it's not IR) would be less of a problem than the flashing LEDs on the front of existing routers.

At that frequency, their retinas couldn't respond fast enough to produce anything but a steady on signal, just like looking at any constant source of light. That is distinct from the flickering of an old 60 Hz fluorescent that most people don't notice but can actually produce a variable signal on the optic nerve.

lower power, possibly. There are benefits to requiring line of sight, as well as drawbacks. You'd need more than one AP for a house, but you wouldn't have to worry about your neighbors stomping on your frequency.

I'd be surprised if it were lower power. RF is very efficient, and detectors very low noise. Basically RF detectors are limited by thermal noise ~1/40 ev, while photo detectors can't measure less than 1 photon (~1ev) and most are ~100X worse than that.

Avoiding frequency congestion would be useful if the bandwidth is competitive with wireless.

The problem is that it isn't a very secure limit unless you are in a light-tight room. If the system is modulating lighting LEDs, then it may possible to snoop on the AC power lines. I could imagine making the lighting system secure, but its not trivial. If you want security there are lots of encryption methods that are much more secure. If you are really worried about snooping (defense work), then you need a certified RF shielded room in any case.

It also requires that you actually want a light in whatever locations you plan to use this.

That might seem like a "But everyone wants light!" thing, but actually the entire concept of lighting an area is something that has a lot of aesthetic complications attached to it that also have to be worked around. Yes, you want light, but you want it from a particular direction, you want it at a particular level, you typically want to be able to turn off some lights at certain times of day and night and turn on o

The only thing I can think of is regulation. Unlike the radio spectrum, the light spectrum is unregulated so no need to worry about running afoul of the FCC and stay under certain power levels/frequency bands/etc. Also it might work in places where Wi-Fi doesn't due to RF interference (microwave oven factory maybe?) but generally there are other ways to fix that. Speaking as someone old enough to remember the colossal failure of IrDA [wikipedia.org] which was based on very similar principles, I don't think this technolo

sort of like anyone with an antenna can monitor wifi traffic (max distance vs. through walls... *shrug* There's tradeoffs). For stuff that isn't essentially broadcast, I would expect encryption, just like (okay, better than) current wifi practice.

Or you can just buy 60ghz gear off the shelf today. The antennas are tiny, provides several gbits per device regardless of the number of devices. It has all of the same properties as visible light except you won't be destracted by it if you don't want the damn lights on.

Agreed, I can't imagine how this would be better than 60GHz. Mind you I don't see a lot of point in either at home. Maybe someday I'll want to instal a device in every room so I can stream 4k video from a mobile device, but it sure as hell won't be anytime soon.

How would micron-LEDs allow more channels? If you are using different frequencies of light you wouldn't need them that small to cover the usable spectrum. If you are planning on resolving each pixel form the receiving device you certainly couldn't use micron sizes over any useful distance?

I suppose it depends what you mean by "useful distance". I can imagine situations in homes or small offices where line-of-sight over quite short distances would be useful. I've had situations in some of my homes where I wanted something faster than WiFi, cable was messy, trunking/channeling was impractical. What if you could bridge those gaps with a pair of LED trancievers, the sensors focussed on the array of transmitters using a lens?

C'on, this is Slashdot. Is it so complex to say that they employ an NRZ modulation using a light carrier, rather than "a bit like Morse Code from a torch"? Is it so difficult to refere to the switching/modulation frequency, or baud rate, rather than "they can also flicker on and off around 1,000 times quicker than the larger LEDs"?

The idea of using a LED light for communication is presented as a novelty in the summary, when all remotes work this way, and even the original 802.11 specs included a PHY layer t